Vehicles with an internal combustion engine are typically equipped with an exhaust gas treatment system for treating the exhaust gas from the engine. The exhaust gas treatment system typically includes a treatment device, such as but not limited to a catalytic converter, a diesel oxidation catalyst, a selective catalytic reduction system, etc., which includes a catalytic composition that reacts with the exhaust gas. The catalytic composition may, for example, reduce nitrogen oxides (NOx) in the exhaust gas to nitrogen and oxygen, oxidize carbon monoxide (CO) in the exhaust gas to carbon dioxide, or oxidize hydrocarbons (HCs) in the exhaust gas to carbon dioxide and water.
Proper control and operation of the exhaust gas treatment systems requires monitoring or sensing the current composition of the exhaust gas. Accordingly, the exhaust gas treatment systems typically include one or more sensors for sensing or sampling the exhaust gas, for one or more components of the exhaust gas. For example, the sensors of the exhaust gas system may sense an oxygen level in the exhaust gas, or a NOx level in the exhaust gas.